Bismuth antimony telluride (BiSbTe₃) is commonly used for thermoelectric generation at temperatures near ambient temperature. Here, we report incorporating reduced graphene oxide (rGO) and Cu₂Se_0.98Te_0.02 into theBi_0.5Sb_1.5Te₃ (BST) (rGO/Bi_0.5Sb_1.5Te₃-xCu₂Se_0.98Te_0.02, where x = 0.0%, 0.1%, 0.3%, 0.5% and 1.0%, in mass) synthesized by a solid-state technique. The dispersion of rGO and Cu₂Se_0.98Te_0.02 into the BST matrix improved carrier transport properties at the grain boundary interfaces and reduced thermal conductivity. Strong electron scattering at large interface barriers was responsible for increased electrical conductivity. The bulk sample of rGO/BST-0.3% Cu₂Se_0.98Te_0.02 (in mass) possessed a low thermal conductivity of 0.76 W·m⁻¹·K⁻¹ at 497 K. Enhanced phonon scattering at grain boundaries between BST and rGO/Cu₂Se_0.98Te_0.02 caused a low thermal conductivity. At 448 K, the highest zT value for rGO/BST-0.3%Cu₂Se_0.98Te_0.02 (in mass) was 1.64, which is 37% higher than the zT value for pure BST (zT = 1.19). Results suggested that incorporating rGO and Cu₂Se_0.98Te_0.02 into the BST matrix effectively improved thermoelectric power generation.